Removing Ice Buildup On The Target; Emissivity Setting Of The Ir Thermometer; Apparent Temperature Setting Limits - Fluke 4181 User Manual

cover. You must use a dry gas for the purge. This means the gas should have a dew
point below -15°C. We recommend nitrogen or dried air. If the gas contains any water
vapor, ice or moisture will form on the target. A relatively low flow rate of 2.4 – 4.8
liters/min (5 – 10 CFH) is recommended for the purge.
Do not leave the target uncovered for more than 5 seconds, since it can cause ice to
form on the target. To make measurements below the dew point, do the following:
1. Put the target cover in place.
2. Adjust the set-point to the desired temperature and allow the instrument to
stabilize at that temperature.
3. Remove the target cover when the target stabilizes.
4. Take a sample
5. Replace the target cover.
3.4.3

Removing Ice Buildup on the Target

If a small amount of ice has formed, you can place the cover back on the target and
allow the purge gas to sublime the ice. If there is more ice or you don't have a purge
available, change the instrument set-point to a temperature equal to or greater than
50°C with the target uncovered. Allow all ice to melt and all water to dry before re-
turning target to use. DO NOT wipe the target.
3.5

Emissivity Setting of the IR Thermometer

The 4180 and 4181 Precision IR Calibrators are calibrated with a radiometric calibra-
tion. This calibration is done with a highly accurate IR thermometer. This IR thermom-
eter has an emissivity setting of 0.950 during the 4180 or 4181 calibration. Therefore,
when calibrating IR thermometers using the 4180 or 4181, it is best practice to use an
IR thermometer emissivity setting of 0.950. Some IR thermometers do not have an ad-
justable emissivity setting. Most of these will have emissivity set as 0.95. In either of
these cases, the apparent emissivity setting of the instrument should also be set to 0.95.
If the IR thermometer being used does not have an emissivity setting of 0.95, the 4180
and 4181 allows adjustment of emissivity (IRT ε, from 0.90 to 1.00). Refer to Section
4 Menu Structure on page 19 for information on how to access IRT ε in the controller
menu.
If you are not certain of the emissivity setting of the IR thermometer you are cali-
brating, consult your IR thermometer's User's Guide or your IR thermometer's
manufacturer.
3.5.1

Apparent Temperature Setting Limits

The IR calibrator is calibrated with an emissivity setting of 0.95. The instruments have
a variable emissivity adjustment that allows the user to vary their apparent emissivity
from 0.90 to 1.00. This setting should match the IR thermometer's emissivity setting. It
is best to use the emissivity setting of 0.95. However, some IR thermometers do not al-
low for an emissivity setting of 0.95. For these instruments, the calibrator's emissivity
setting should be set to the IR thermometer's emissivity setting. Due to safety issues
Quick Start
Emissivity Setting of the IR Thermometer
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